Claims
- 1. A method of calculating an index k for encoding a sound signal according to a Code-Excited Linear Prediction technique using a sparse algebraic code to generate an algebraic codeword in the form of an L-sample long waveform comprising a small number N of non-zero pulses each of which is assignable to different positions in the waveform to thereby enable composition of several of algebraic codewords A.sub.k, said index calculating method comprising the steps of:
- (a) calculating a target ratio
- (DA.sub.k.sup.T /.alpha..sub.k).sup.2
- for each algebraic codeword among a plurality of said algebraic codewords A.sub.k ;
- (b) determining the largest ratio among said calculated target ratios; and
- (c) extracting the index k corresponding to the largest calculated target ratio;
- wherein, because of the algebraic-code sparsity, the computation involved in said step of calculating a target ratio is reduced to the sum of only N and N(N+1)/2 terms for the numerator and denominator, respectively, namely ##EQU10## where: i=1, 2, . . . N;
- S(i) is the amplitude of the i.sup.th non-zero pulse of the algebraic codeword A.sub.k ;
- D is a backward-filtered version of an L-sample block of said sound signal;
- p.sub.i is the position of the i.sup.th non-zero pulse of the algebraic codeword A.sub.k ;
- p.sub.j is the position of the j.sup.th non-zero pulse of the algebraic codeword A.sub.k ; and
- U is a Toeplitz matrix of autocorrelation terms defined by the following equation: ##EQU11## where: m=1, 2, . . . L; and
- h(n) is the impulse response of a transfer function H varying in time with parameters representative of spectral characteristics of said sound signal and taking into account long term prediction parameters characterizing a periodicity of said sound signal.
- 2. A method as defined in claim 1, wherein the step of calculating the target ratio
- (DA.sub.k.sup.T /.alpha..sub.k).sup.2
- comprises:
- calculating in N successive embedded computation loops contributions of the non-zero pulses of the algebraic codeword A.sub.k to the denominator of the target ratio; and
- in each of said N successive embedded computation loops adding the calculated contributions to contributions previously calculated.
- 3. A method as defined in claim 2, wherein said adding step comprises adding the contributions of the non-zero pulses of the algebraic codeword A.sub.k to the denominator of the target ratio calculated in the embedded computation loops by means of the following equation: ##EQU12## in which SS(i,j)=S(i)S(j), said equation being developed as follows: ##EQU13## where the successive lines represent contributions to the denominator of the target ratio calculated in the successive embedded computation loops, respectively.
- 4. A method as defined in claim 3, in which said N successive embedded computation loops comprise an outermost loop and an innermost loop, and in which said contribution calculating step comprises calculating the contributions of the non-zero pulses of the algebraic codeword A.sub.k to the denominator of the target ratio from the outermost loop to the innermost loop.
- 5. A method as defined in claim 3, further comprising the step of calculating and pre-storing the terms S.sup.2 (i) and SS(i,j)=S(i)S(j) prior to said step (a) for increasing calculation speed.
- 6. A method as defined in claim 1, further comprising the step of interleaving N single-pulse permutation codes to form said sparse algebraic code.
- 7. A method as defined in claim 1, wherein the impulse response h(n) of the transfer function H accounts for
- H(z)=F(z)/(1-B(z))A(z.gamma..sup.-1)
- where F(z) is a first transfer function varying in time with parameters representative of spectral characteristics of said sound signal, 1/(1-B(z)) is a second transfer function taking into account long term prediction parameters characterizing a periodicity of said sound signal, and A(z.gamma..sup.-1) is a third transfer function varying in time with said parameters representative of spectral characteristics of said sound signal.
- 8. A method as defined in claim 7, wherein said first transfer function F(z) is of the form ##EQU14## where .gamma..sub.1.sup.-1 =0.7 and .gamma..sub.2.sup.-1 =0.85.
- 9. A method as defined in claim 1, further comprising the following steps for producing the backward-filtered version D of the L-sample block of said sound signal:
- whitening the L-sample block of said sound signal with a whitening filter to generate a residual signal R;
- computing a target signal X by processing with a perceptual filter a difference between said residual signal R and a long-term prediction component E of previously generated segments of a signal excitation to be used by a sound signal synthesis means to synthesize said sound signal; and
- backward filtering the target signal X with a backward filter to produce said backward-filtered version D of the L-sample block of said sound signal.
- 10. A system for calculating an index k for encoding a sound signal according to a Code-Excited Linear Prediction technique using a sparse algebraic code to generate an algebraic codeword in the form of an L-sample long waveform comprising a small number N of non-zero pulses each of which is assignable to different positions in the waveform to thereby enable composition of several algebraic codewords A.sub.k, said index calculating system comprising:
- (a) means for calculating a target ratio
- (DA.sub.k.sup.T /.alpha..sub.k).sup.2
- for each algebraic codeword among a plurality of said algebraic codewords A.sub.k ;
- (b) means for determining the largest ratio among said calculated target ratios; and
- (c) means for extracting the index k corresponding to the largest calculated target ratio;
- wherein, because of the algebraic-code sparsity, the computation carried out by said means for calculating a target ratio is reduced to the sum of only N and N(N+1)/2 terms for the numerator and denominator, respectively, namely ##EQU15## where: i=1, 2, . . . N;
- S(i) is the amplitude of the i.sup.th non-zero pulse of the algebraic codeword A.sub.k ;
- D is a backward-filtered version of an L-sample block of said sound signal;
- p.sub.i is the position of the i.sup.th non-zero pulse of the algebraic codeword A.sub.k ;
- p.sub.j is the position of the j.sup.th non-zero pulse of the algebraic codeword A.sub.k ; and
- U is a Toeplitz matrix of autocorrelation terms defined by the following equation, ##EQU16## where: m=1, 2, . . . L
- h(n) is the impulse response of a transfer function H varying in time with parameters representative of spectral characteristics of said sound signal and taking into account long term prediction parameters characterizing a periodicity of said sound signal.
- 11. A system as defined in claim 10, wherein said means for calculating the target ratio
- (DA.sub.k.sup.T /.alpha..sub.k).sup.2
- comprises N successive embedded computation loops for calculating contributions of the non-zero pulses of the algebraic codeword A.sub.k to the denominator of the target ratio, each of said N successive embedded computation loops comprising means for adding the calculated contributions to contributions previously calculated.
- 12. A system as defined in claim 11, wherein each of said N successive embedded computation loops comprises means for adding the contributions of the non-zero pulses of the algebraic codeword A.sub.k to the denominator of the target ratio by means of the following equation: ##EQU17## in which SS(i,j)=S(i)S(j), said equation being developed as follows: ##EQU18## where the successive lines represent contributions to the denominator of the target ratio calculated in the successive embedded computation loops, respectively.
- 13. A system as defined in claim 12, in which said N successive embedded computation loops comprise an outermost loop, an innermost loop, and means for calculating the contributions of the non-zero pulses of the algebraic codeword A.sub.k to the denominator of the target ratio from the outermost loop to the innermost loop.
- 14. A system as defined in claim 12, further comprising means for calculating and pre-storing the terms S.sup.2 (i) and SS(i,j)=S(i)S(j) for prior to the target ratio calculation for increasing calculation speed.
- 15. A system as defined in claim 10, wherein said sparse algebraic code consists of a number N of interleaved single-pulse permutation codes.
- 16. A system as defined in claim 10, wherein the impulse response h(n) of the transfer function H accounts for
- H(z)=F(z)/(1-B(z))A(z.gamma..sup.-1)
- where F(z) is a first transfer function varying in time with parameters representative of spectral characteristics of said sound signal, 1/(1-B(z)) is a second transfer function taking into account long term prediction parameters characterizing a periodicity of said sound signal, and A(z.gamma..sup.-1) is a third transfer function varying in time with said parameters representative of spectral characteristics of said sound signal.
- 17. A system as defined in claim 16, wherein said first transfer function F(z) is of the form ##EQU19## where .gamma..sub.1.sup.-1 =0.7 and .gamma..sub.2.sup.-1 =0.85.
- 18. A system as defined in claim 10, further comprising:
- a whitening filter for whitening the L-sample block of said sound signal with a whitening filter to generate a residual signal R;
- a perceptual filter for computing a target signal X by processing a difference between said residual signal R and a long-term prediction component E of previously generated segments of a signal excitation to be used by a sound signal synthesis means to synthesize said sound signal; and
- a backward filter for backward filtering the target signal X to produce said backward-filtered version D of the L-sample block of said sound signal.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2010830 |
Feb 1990 |
CAX |
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Parent Case Info
This is a Continuation of U.S. patent application Ser. No. 07/927,528 filed on Sep. 10, 1992, U.S. Pat. No. 5,444,816, and entitled "Dynamic codebook for efficient speech coding based on algebraic codes".
US Referenced Citations (26)
Foreign Referenced Citations (1)
Number |
Date |
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0 138 061 A1 |
Apr 1985 |
EPX |
Continuations (1)
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Parent |
927528 |
Sep 1992 |
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